1. Field of the Invention
The present invention relates generally to a spark ignition timing control system for an internal combustion engine. More specifically, the invention relates to a technique for suppressing or reducing uncomfortable shock upon engine acceleration, by controlling spark ignition timing.
2. Description of the Background Art
The recent automotive internal combustion engine have significantly improved acceleration characteristics by development of an electronic fuel injection control system which has substantially high response to engine acceleration demand. Therefore, engine revolution speed tends to rapidly increases output torque. This creates acceleration shock upon initiation of engine acceleration.
On the other hand, because of heavy weight of vehicular body, relatively great inertia moment is exerted on the vehicle body to lower response characteristics in vehicular acceleration. In relation to rapid engine acceleration, jerking tends to occur upon vehicular acceleration. Furthermore, during transition from engine acceleration state to steady state, uncomfortable pitching vibration occurs by causing longitudinal shift of the gravity center.
In order to suppress such uncomfortable vehicular jerking and pitching vibration, the co-pending U.S. patent application Ser. No. 170,360, filed on Mar. 18, 1988, still pending, and assigned to the common assignee to the present invention, proposes control of spark advance for suppressing too rapid engine speed variation for suppressing shock during engine acceleration and deceleration. For instance, upon engine acceleration, spark advance is retarded in a predetermined retarding angular magnitude for making increase of the engine output torque moderate enough to facilitate smooth acceleration.
In opposition to requirement for prevention of uncomfortable jerking and pitching vibration during acceleration, it is also important factor for providing better engine performance to provide good engine acceleration characteristics. Therefore, in spark ignition timing control, it becomes essential to balance prevention of vehicular jerking and/or pitching and satisfactory acceleration characteristics.